Chemical vapor deposition processes are used to continuously coat glass substrates while the glass is being manufactured in what is generally known in the art as the float glass process. The float glass process typically involves casting glass onto a molten tin bath which is suitably enclosed, then transferring the glass, after it has sufficiently cooled, to lift out rolls which are aligned with the bath, and finally cooling the glass as it advances across the rolls through a lehr. The chemical vapor deposition of various coatings may conveniently be performed in the bath, the lehr, or the transition zone therebetween.
Chemical vapor deposition generally involves the formation of a metal, metal compound, or metal oxide coating, or combination thereof, on a surface of a hot glass substrate by contacting the surface with a gaseous mixture or precursor containing a vaporized substance which undergoes a chemical reaction or decomposition. Such coatings are generally applied to modify the apparent color or solar characteristics of the glass, such as in the application of a reflection/absorption filter band to an automobile windshield, or to impart electrical conductance to the surface of the glass. One such use for the latter mentioned coating is the production of a rain sensor on the exterior surface of an automotive windshield.
Occasionally, the area which must be coated is substantially smaller than the entire surface of the glass ribbon produced by the float glass process. Such an example is the small area which must be coated in order to produce the aforementioned rain sensor, in relation to the total surface area of an automotive windshield. It is generally known that a rain sensor may be prepared by coating the entire glass surface with a doped tin oxide coating to a 100 ohm/square conductivity utilizing a conventional float glass process CVD coater which spans the entire width of the glass ribbon, and thereafter removing, by etching or vaporizing, the unwanted portion of the conductive coating. This, however, is wasteful of coating chemicals and etching solutions, and unnecessarily increases the time required to produce a windshield having a rain sensor.
One solution to this dilemma might be to apply a coating of the required material in the form of a stripe on the continuously produced glass ribbon manufactured by the float glass process. Then the amount of coating to be removed from the finished article would be greatly reduced. However, a conventional CVD coater could not be used because it is designed to "ride" on the edges of the glass ribbon, utilizing such as for example carbon fiber seals which contact and slide over the advancing glass ribbon. These edge portions of the glass, which are marred by contact with the coater side seals, are later removed. Generally, the front and back edges of a conventional CVD coater are each superposed over the top surface of the advancing glass ribbon, thereby defining narrow gaps through which gases exterior from the coater may be drawn so as not to contaminate the controlled atmosphere within the float glass facility. This is particularly important when CVD coating a metal oxide within the bath, where the molten tin might otherwise be contaminated by CVD oxidation reactants. If such a conventional coater were modified to produce only a stripe of CVD coated material, the defects caused by the side seals sliding on either side of the applied stripe would render the entire glass ribbon useless.
U.S. Pat. No. 4,776,298 discloses an apparatus for performing plasma enhanced chemical vapor deposition of a metal oxide coating at the edge of a polycarbonate sheet. The seal which maintains the CVD reactants within the deposition zone, however, is formed by contact between the coater body and the polycarbonate sheet surface. Therefore, such a device could not be utilized in conjunction with the float glass process without damaging the surface of the glass upon which the seal rests.
U.S. Pat. No. 4,278,528 discloses a method and apparatus for applying stripes of coating material onto a moving substrate, by a sputtering technique in which a mask, defining the widths of the stripes, is interposed between the targets and the anodes.
U.S. Pat. No. 4,562,093 discloses a process for the production of glass sheets for windshields having a reflection/absorption filter band thereon, using a cathode atomization sputtering apparatus and a shutter arrangement to adjust the width of the deposited stripes.
It would be desirable to construct a coater apparatus which could be used to apply a stripe of coating material onto an advancing glass ribbon being produced by the float glass process, by chemical vapor deposition, which apparatus would not contact and thereby mar the surface of the glass, nor utilize inconvenient masks or shutters, and which would provide a seal so as to prevent the escape of vaporized reactants to the exterior of the coater.
It must be noted that the prior art referred to herein above has been collected and reviewed only in light of the present invention as a guide. It is not to be inferred that such diverse art would otherwise be assembled absent the motivation provided by the present invention.